Many automotive components are made from reinforced and unreinforced plastics. Weight savings are achieved by using hollow cores in the plastic molding processes for making such components. Core elements for such molded parts are generally tubular metal or solid foam thermoplastic materials. Because of the complex shapes of the molded articles and cores used to make automotive components, the cores are generally not removable, and therefore are left encapsulated in the finished molded part. Thus, molders have been motivated to use lighter-weight core materials, to reduce the overall weight of the ultimately produced articles.
U.S. Pat. No. 5,169,590 discloses the use of flexible blow molded thermoplastic cores in resin molding processes. The cores are retained in, and add weight to, the ultimately produced molded parts. The temperatures at which the parts may be molded are limited by the softening temperatures of the thermoplastic cores utilized. Moreover, if the thermoplastic cores are excessively preheated in the molds, lower injection pressures must be used to prevent surface deflection of the core elements.
U.S. Pat. Nos. 4,610,836 and 4,695,343 disclose a method for preparing a reinforced molded article utilizing a structural core comprising adhesively bonded glass macrospheres. The glass macrospheres become adhesively bonded to the molded article to reinforce same. The core is retained in, and adds weight to, the ultimately produced molded part.
It would be desirable to mold plastic components using cores which allow high temperature and/or high pressure molding conditions, while eliminating the added weight of the core material in the ultimately produced molded parts.